For the microstructured functionalisation or coating of surfaces of foil substrates, conventionally the substrate is placed between two planar electrodes and the system is closed like a die over the foil via a stroke mechanism. One of the electrodes thereby has microstructures in which a plasma is then formed selectively during application of a high voltage. After the treatment, the system is opened again and the foil is guided a little further and subsequently a further part of the foil is treated in a corresponding manner. The method is therefore implemented in a batch process (batch treatment).
It is known for continuous treatment of a surface of a foil that a roller with a coarse structure opposite which an electrode is disposed can be used. A roller with different structural depths is provided here. The structures are then filled with a dielectric. On the side orientated away from the roller, a selective plasma can then be ignited. Hence a selective treatment of that foil side which is orientated away from the roller is possible. However, the roller structure requires a high aspect ratio of up to several millimeters so that, precisely in the case of process gases, such as nitrogen and noble gases, sharp delimitations of the structures can no longer be achieved. This resides mainly in the fact that a spatial glow discharge (also known as atmospheric plasma glow discharge) in the noble gases results. In the case of nitrogen as process gas, very long-lived reactive species which can also functionalise or treat those regions of the surface which are not subjected directly to the plasma are produced. A further disadvantage of these methods is that an undesired rear-side treatment of the foil can result.